Some bacteria (Shigella, Campylobacter, and Salmonella), viruses (hepatitis A, B, and C), and parasites (Giardia and some amebas) are sometimes transmitted during sexual intercourse, although they are typically transmitted in other ways. These organisms, except for hepatitis B and C viruses, typically infect the digestive tract and are acquired when people consume contaminated food or water. In the digestive system, the organisms multiply and are excreted from the body in the feces. They can be spread through contact with the anus or feces of an infected person—for example, during anal sex.
Symptoms vary depending on the organism. They may include diarrhea, fever, abdominal pain or bloating, nausea, vomiting, and jaundice.
Infections recur frequently, especially in homosexual men with many sex partners. Some infections cause no symptoms but may have serious long-term complications, such as chronic hepatitis B or C.
Resource: Merck Manual Home Edition